1. Field of the Invention
The present invention relates to an electron-emitting device, particularly an electron-emitting device which can maintain stable electron emission for a long time, an electron source using the electron-emitting devices, an image-forming apparatus, such as a display device and an exposure device, using the electron source, as well as manufacture methods for the electron-emitting device, the electron source, and the image-forming apparatus.
2. Related Background Art
There are hitherto known two major types of electron-emitting devices; i.e., thermionic cathode type electron-emitting devices and cold cathode type electron-emitting devices. Cold cathode type electron-emitting devices include the field emission type (hereinafter abbreviated to FE), the metal/insulating layer/metal type (hereinafter abbreviated to MIM), the surface conduction type, etc.
Examples of FE electron-emitting devices are described in, e.g., W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976).
One example of MIM electron-emitting devices is described in, e.g., C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 (1961).
One example of surface conduction electron-emitting devices is described in, e.g., M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965).
Surface conduction electron-emitting devices operate based on such a phenomenon that when a thin film of small area is formed on a base plate and a current is supplied to flow parallel to the film surface, electrons are emitted therefrom. As to such surface conduction electron-emitting devices, there have been reported, for example, one using a thin film of SnO.sub.2 by Elinson cited above, one using an Au thin film [G. Dittmer: Thin Solid Films, 9, 317 (1972)], one using a thin film of In.sub.2 O.sub.3 /SnO.sub.2 [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)], and one using a carbon thin film [Hisashi Araki et al.: Vacuum, Vol. 26, No. 1, 22 (1983)].
As a typical example of those surface conduction electron-emitting devices, FIG. 20 schematically shows the device configuration proposed by M. Hartwell; et al. in the above-cited paper. In FIG. 20, denoted by reference numeral 1 is a substrate (hereinafter, it is refered as "a base plate"). 4 is an electroconductive thin film formed of, e.g., a metal oxide thin film made by sputtering into an H-shaped pattern, in which an electron-emitting region 5 is formed by energization treatment called energization forming (described later). Incidentally, the spacing L between opposed device electrodes is set to 0.5-1 mm and the width W of the electroconductive thin film is set to 0.1 mm.
In those surface conduction electron-emitting devices, it has heretofore been customary that, before starting the emission of electrons, the electron-emitting region 5 is previously formed by energization treatment called energization forming. Specifically, the term "energization forming" means treatment of applying a DC voltage or a voltage gradually increasing at a very slow rate of about 1 V/minute, for example, across the electroconductive thin film 4 to locally destroy, deform or denature it to thereby form the electron-emitting region 5 which has been transformed into an electrically high-resistant state. In the electron-emitting region 5, an electron emitting region is produced in part of the electroconductive thin film 4 and electrons are emitted from the vicinity of the fissure.
Since the above surface conduction electron-emitting devices are simpler in structure and can relatively easily be formed in a large number at a high density, their application to image-forming apparatus or the like is expected. If stable electron emission is continued for a long time and characteristics and efficiency of electron emission are improved, it will be possible in image-forming apparatus using a fluorescent film as an image-forming member, by way of example, to realize low-current, bright and high-quality apparatus, e.g., flat TV units. Also, with a lowering in current required, the cost of a driving circuit and so on making up the image-forming apparatus can be cut down.
However, the aforementioned electron-emitting device proposed by M. Hartwell et al. is not sufficiently satisfactory in points of stable electron emission characteristics and efficiency. Thus, it is very difficult in the state of art to provide image-forming apparatus, which has high luminance and excellent stability in operation, by using such electron-emitting devices.